This invention relates to an alternator assembly which can provide an output to a plurality of loads and more particularly, although not exclusively, which is operable to provide an initial voltage output sufficient to initiate conduction of each of a plurality of high intensity lamps to be energised followed by a sustaining voltage output to maintain current flow in each of the lamps after the initial conduction.
U.S. Pat. No. 5,808,450 discloses a lighting system which eliminates the need for ballast and voltage regulation in the system by providing an alternator assembly having internal impedance characteristics significantly and substantially above the conventional impedance and by transmitting electrical AC power preferably at a high frequency (say between 200-600 Hz and more particularly between 500-550 Hz) from the alternator usable for direct connection to an associated lamp. In a mobile light tower application, the system preferably has a plurality of lamps and each lamp has a dedicated alternator winding which outputs electrical AC power suitable for direct supply to that lamp. Each winding is preferably formed as a part of a separate alternator unit having its rotor and high impedance output windings. However, an alternator assembly may be provided in which a stator is wound with an appropriate plurality of individual dedicated stator windings, one for each of the lamps to be energised. This would imply the use of a poly-phase machine, one phase for each of the lamps to be energised. However, a poly-phase system operating on a common magnetic circuit would be exposed to inherent mutual inductance between phases. For example, if four lamps were used, this would be proportional to the cosine of 45 degrees (0.707). Thus the reactance of the phases would change and, hence, the luminescence output from each lamp, depending on the number of lamps energized at any one time.
U.S. Pat. Nos. 6,094,011 and 6,239,552 each disclose a discharge lamp lighting system, which does not require ballast between the generator and the lamps wherein the generator includes a plurality of generating coils, one for each lamp, the generating coils being electrically independent from each other. Also a stator of the generator is provided with means by which each of the generating coils is substantially kept from flow of magnetic flux interlinking the other generating coils through the magnetic circuit.
U.S. Pat. No. 4,996,457 discloses a permanent magnet axial flux alternator having a rotor disc between a pair of annular stator discs. Each stator disc carries a winding which has its output connected to a respective load. A magnetic isolator within the rotor isolates the magnets on each side of the rotor and thus isolates each stator disc so that operation of the load connected to one of the stator discs does not affect any operation in the load connected to the other stator disc.
Two forms of alternator assembly which embody this invention and which are for use in a portable light tower are described now by way of example with reference to the specification and the accompanying drawings.